There are many differences between these two systems. Some of the most important are:

The people get to play a part in choosing their leaders in a democracy. In a dictatorship, they do not.

The rights of the people are protected in a democracy. In a dictatorship, they are not.

In a democracy, the powers of the government are limited. There is typically a constitution that says what the government can and cannot do. It is a "government of laws." In a dictatorship, there are no limits on what government can do. It is a "government of men" where the rulers can do whatever they want so long as the dictator agrees.